Boiler having gas-tight welded furnace walls

ABSTRACT

A boiler mounted on a supporting frame structure has gas-tight welded furnace walls suspended at the top of the frame structure and arranged to form a furnace of rectangular cross-section wherein heat is generated when the boiler is operating. A member is connected to the walls and introduces a discontinuity therein. A plurality of horizontal bands surrounding the walls to take up the expansion and contraction forces developed therein because of the heat generated in the furnace and each of the horizontal bands consist of four segments connected one with the other to form a substantially rectangular figure, the segments being rigidly joined at their ends to form the corners of the figure. At least one additional band is disposed in the upper region of the member and a holding means connects the furnace walls to the additional band at the corners thereof so as to cause the walls to take up the portion of the forces acting in the region of the member. A force transfer means is connected between the plurality of bands and the furnace walls for guiding the boiler body in the plurality of bands so as to pretension the walls of the furnace so as to cause the walls to define obtuse angles at the corners of the furnace when there is no heat being developed therein, the angles being selected so as to cause the angles to become right angles as well as to cause the walls to extend parallel to adjacent band segments when the furnace is heated.

United States Patent 1 Michel Sept. 25, 1973 BOILER HAVING GAS-TIGHT WELDED FURNACE WALLS [75] Inventor: Rupprecht Michel, Erlangen,

Germany [73] Assignee: Kraftwerk Union Aktiengesellschaft,

Mulheim (Ruhr), Germany [22] Filed: Nov. 15, 1971 [21] Appl. No.: 198,698

[30] Foreign Application Priority Data Primary Examinerl(enneth W. Sprague Art0rneyArthur E. Wilfond et al.

[57] ABSTRACT A boiler mounted on a supporting frame structure has gas-tight welded furnace walls suspended at the top of the frame structure and arranged to form a furnace of rectangular cross-section wherein heat is generated when the boiler is operating. A member is connected to the walls and introduces a discontinuity therein. A plurality of horizontal bands surrounding the walls to take up the expansion and contraction forces developed therein because of the heat generated in the furnace and each of the horizontalbands consist of four segments connected one with the other to form a substantially rectangular figure, the segments being rigidly joined at their ends to form the corners of the figure. At least one additional band is disposed in the upper region of the member and a holding means connects the furnace walls to the additional band at the corners thereof so as to cause the walls to take up the portion of the forces acting in the region of the member. A force transfer means is connected between the plurality of bands and the furnace walls for guiding the boiler body in the plurality of bands so as to pretension the walls of the furnace so as to cause the walls to define obtuse angles at the corners of the furnace when there is no heat being developed therein, the angles being selected so as to cause the angles to become right angles as well as to cause the walls to extend parallel to adjacent band segments when the furnace is heated.

10 Claims, 4 Drawing Figures BOILER HAVING GAS-TIGHT WELDED FURNACE WALLS The invention relates to a large boiler having a boiler body suspended from the top of a boiler frame. The

boiler body is configured of tubes which are joined gastight with one another. The boiler body has a rectangular or square cross-section. In such boilers, the wall planes are strengthened by means of a frame construction located behind the tube walls. The frame construction consists primarily of bands which do not become heated and extend horizontally and vertically.

Large boilers with gas-tight welded furnace walls of the conventional type are driven with high-pressure firing and are for the most part configured so that the low and high pressures obtained in the combustion chamber are taken up by horizontally extending bands. These bands take up the forces in the corners of the combustion chamber with hinged members and tie rods which become heated or with tubes through which steam passes and transfer these forces to the opposite lying sides. Insofar as the strength of the walls permits, these forces are transmitted via the walls.

When the boiler is brought into operation, the welded furnace walls are gradually heated and undergo intense expansion. This expansion takes place with respect to the horizontal bands which remain cool and is made possible by slide means or by' hinged members. The application of hinged members which are heated or tie rods through which steam flows and their location behind the welded furnace wall as well as the application of hinged members in the region of the combustion chamber corners not only is very costly, but also, in some circumstances, restricts the speed with which the boiler can be brought up to the operating condition, because the hot tie rods become warm at a considerably slower rate than does the tube wall itself.

In order to make the construction of the boiler less expensive, attempts have already been made to do without the hot tie rods behind the tube wall and to hold the bands which remain cool together with shockabsorbers in the corners of the combustion chamber. Also, limit screws are provided which under full load and full heat expansion of the welded walls become pulled up in a force-locked manner. This applies also to furnace walls wherein the tubes are arranged vertically as well as for walls wherein the boiler tubes are arranged in spiral configuration.

Such solutions have been found to be unsatisfactory because the shock absorbers in the corners of the combustion chambers are in a position to 'take up only ex pansions that occur for a short time. And the parallel lying limit screws provide a force-locked connectiononly for the expansion corresponding to full load. For partial loading especially when operating under varying pressure, the boiler body expands to a lesser'degree, so that the limit screws in the'corners are notapplied in force-locking condition. This leads to undesirable vibration of'the combustion chamber corners and to a deflection of the'hinged members on which the shock absorbers are suspended. i

It is an object of the invention to provide a boiler that overcomes the foregoing disadvantages. It is another object of the invention to provide a boiler that can be operated at various firing pressures as well as shift rapidly from one firing pressure to another and still take up the various degrees of epansion and contraction associated therewith without difficulty.

According to a feature of the invention a plurality of horizontal bands are joined lock-tight in the corners while in the unheated condition and the rigid frames formed in this manner have such an inner dimension that the boiler body at full load just fits directly or with unyielding intermediate members therein. The displacement of the tube wall which expands when heated is made possible by sliding means, hinged members or the like. The walls are pre-tensioned in the corners of the furnace that is, they are installed so that the walls coming together at the corners define a small obtuse angle. Whentheboiler is brought into operation, the combustion chamber walls expand toward the corners, so that these corners then form a right angle.

The forces arising because of under and overpressures are transmitted in every operational condition by the bands. These bands are not heated and are rigidly joined at their corners. This eliminates the need for the bands which became heated and which were considered previously as necessary or also the steam carrying tubes which were used in their place as well as all hinged members with which cold bands were previously articulately joined in. the combustion chamber corners. To limit or hold the bending of the tube walls within limits, it is recommended that the final connection of the tube walls with respect to the horizontal bands be provided by articulated or hinged arms which, for example, can be arranged from one to two meters from the corners and which stand in the unheated condition at a slanted angle. This angle is dependentupon the width of the furnace wall and the spacing of the unheated bands from the tube wall.

During the assembly, the furnace corners can be put together with pre-tensioning such that they have the required spacing at each side for the expansion at full load condition. Such spacing, for example, can be approximately 50 mm to each side for a large boiler having a furnace cross-section of approximately 20 by 20 meters. When the boiler heats up,'bending occurs in the corner region which remains within the elastic deformation limit.

Of course at such locations of the furnace at which a hopper intake begins or a flat furnace floor is built in, the strengthening or reinforcement in this place must, as is conventional, be achieved by bands which stay. cold. In the known manner, these bands are joined at their corners with the boiler system or tie-rods via hinged members. In the event that the boiler is equipped with a furnace hopper the outer reinforcem'ent construction of the furnace hopper can likewise be configured in the corners so as to be completely rigid. This rigid hopper construction can be suspended via pendular arms from notched plates which are welded at the hopper edge of the tubesystem and serve simultaneously to transfer the hopper load over stationary hangers to vertical iron members disposed behind the tube wall. The horizontal and vertical expansion of the tube system locatedin the furnace hopper can also be made possible in that the corners of thetube system are bent backward to the extent that, in the full load operational condition, the gas-tight welded tube system in the furnace hopper can expand into the stationary hopper frame via the built-in horizontal and vertical slidable spacer members. The walls in the region of the convection heat surfaces can also be braced'against horizontal bands rigidly joined in the corners; however, the various inlet and outlet collectors of the convection heat surfaces in the region of the corners of this singleflue boiler must be subdivided many times so that the convection heat surfaces welded into the corners are in a position to move with the walls. In boiler installations which are provided with suction flue ventilators, that is, those driven at under pressure, the heat convection surfaces in the corner regions can also be directed via stuffing boxes through the walls and then the inlet and outlet collectors of these heat surfaces need not be subdivided.

Although the invention is illustrated and described herein as a large boiler with gas-tight welded furnace walls, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein within the scope and the range of the claims. The invention, however, together with additional objects and advantages, will be best understood from the following description and in connection with the accompanying drawings, in which:

FIG. 1 schematically illustrates a rigid corner joint of the horizontal bands;

FIG. 2 is a perspective view showing the expansion of a tube system at the region of the ash hopper;

FIG. 3 illustrates the suspension of the outer reinforcement structure as required by one embodiment of the invention; and

FIG. 4 illustrates schematically the total assembly of a large boiler according to the invention.

FIG. 1 illustrates arigid corner joint of a horizontal band which forms a closed frame. The two horizontal band segments 1 and 2 are joined tightly to each other by means of screws 3 and 4. At the remaining corners, a similar joint of the band segments is made.

Of the boiler body, only the furnace walls 5 and 6 are shown; these walls mutually abut and the tubing, for example, is configured as a spiral winding. Directly behind the tube wall are disposed vertically extending flat iron members 7 which, for example, are slidably mounted on the tube wall and serve, among other things, to carry the weight of the horizontal bands.

The walls 5 and 6 are illustrated in their unheated or cold condition. Compared to the horizontal band segments 1 and 2 and also compared to the inner bottom edge of the furnace in the cold condition (illustrated by line 8), the boiler body in the unheated condition is curved or bent as illustrated in FIG. 1 wherewith, especially in the region of the furnace corners 9, there is a small obtuse angle. As soon as the boiler body has reached its operating temperature, the furnace walls will have become extended to the extent that the boiler body takes on a position approximately as indicated by line 10. The corners 9 then form a right angle.

Reference numerals 11, 12, 13 and 14 designate hinged arms which are installed between the boiler body and horizontal band segments 1 and 2. The hinged arms 12 and 13 are disposed approximately 1 to 2 meters from the corner and these arms then form such an angle in the cold condition that the furnace walls define a right angle in the operating condition as shown by line 10. The double T irons 15 serve to accommodate additional hinged arms above and beneath the horizontal band comprising band segments 1 and 2. FIG. 2 illustrates the expansion of the welded tube system in the region of the ash hopper 16 in the cold condition (solid line 21) and in the heated condition (dashed line 22). The expansion indicated by the dashed lines is exaggerated for the purpose of illustration. The hatched surfaces 17 and 18 on two sides of the hopper 16 illustrate the regions in which the heating causes no deformation and where only marginally small displacements occur. That is, the hatched region indicates where the tube walls, in the cold condition as well as in the warm condition, are guided at a constant spacing via hinged arms with respect to the rigid frame structure of the hopper, the latter structure remaining in the cold condition. The edge zones 19, 20, 23 to 26 outside the hatched surfaces 17 and 18 bend slightly in form with the transition from the cold to the heated condition and vice versa as represented by lines 21 and 22. During assembly, the corners are built in with a measure of pretensioning and with a small obtuse angle precisely as in the case of the vertical walls. When the boiler is brought into operation, the tube system presses into the corners and forms thereat a right angle. Simultaneously therewith, the tube system becomes displaced downwardly into the hopper frame as a consequence of its expansion and is thereby correspondingly pressed together. Also, the hopper slit, located at the bottom thereof and not illustrated in the drawing, is deformed during heating to the operating temperature. The hopper slit is likewise built in with pretensioning, so that the slit edges form parallel straight lines at full operating temperature.

FIG. 3 illustrates an embodiment for suspending the outer reinforcement structure of the hopper. The horizontal bands 27 to 32 with vertical flat iron members 33 to 41 are hung via hinged arms 44 and stationary hangers 42 to the hopper edge 43. Thestationary hangers 42 transfer the load of the hopper and the weight of the ash collected therein to the flat irons 7 which lie directly behind the vertical tube walls 5 and 6 (see FIG. 1). The hinged arms 45 permit a vertical and horizontal displacement of the hopper in the rigid frame.

FIG. 4 illustrates schematically the complete assembly of an embodiment of a large boiler according to the invention. All the horizontal bands 51 to 55 and 57 to 60 are configured as rigid bands, for which the hinged arms in the corners are unnecessary, and which are therefore in a position to take up the forces occurring as a consequence of under and over pressure. Only in the region of band 56 at the elevation of the top edge of the hopper, which edge is joined in the conventional manner to the tube walls via hinged arms, are the forces produced by over and under pressures transmitted by the wall itself.

I claim:

1. A boiler assembly comprising a supporting frame structure, a boiler mounted on said frame structure and comprising gas-tight welded furnace walls, means suspending said walls at the top of the frame structure, said walls being arranged to form a furnace of a rectangular cross-section wherein means are provided for generating heat when the boiler is operating, a member connected to said walls and introducing a discontinuity therein, a plurality of horizontal bands surrounding said walls to take up the expansion and contraction forces developed therein because of the heat generated in the furnace, each of said horizontal bands consisting of four segments connected one with the other to form a substantially rectangular figure, said segments being rigidly joined at their ends to form the corners of said figure, at least one additional band being disposed in the region of said member, holding means connected to said furnace walls and to said one band at the corners thereof so as to cause said walls to take up the portion of said forces acting in the region of said member, force transfer means connected between said plurality of bands and said furnace walls for guiding the boiler body in said plurality of bands so as to pretension said walls I of said furnace so as to cause said walls to define obtuse angles at the corners of said furnace when there is no heat being developed therein, said angles being selected so as to cause said angles to become right angles as well as to cause said walls to extend parallel to adjacent band segments when said furnace is heated.

2. A boiler assembly according to claim 1, said holding means being movable intermediate members and said force transfer means being a plurality of sets of articulate arms, the arms of each set being connected between corresponding bands of said plurality of bands and said furnace walls.

3. A boiler assembly according to claim 1, said holding means being hinged arms. I

4. A boiler assembly according to claim 1, comprising tie rods disposed behind said walls and connected to said holding means for taking up said portion of said forces.

5. A boiler assembly according to claim 1, comprising tubular tie rods disposed behind said walls and connected to said holding means for taking up said portion of said forces, and means communicating with said tubular tie rods for passing steam therethrough.

6. A boiler assembly according to claim 1, said one additional band consisting of four segments arranged to form a substantially rectangular figure and being'open at the corners of said figure, said holding means comprising articulate arms connecting said segments at the respective corners of said figure to cause said furnace walls to take up said portion of said forces.

7. A boiler assembly according to claim 1, said force transfer means comprising sets of articulated arms connecting respective ones of said plurality of bands with said furnace walls atvthe region of the corners of said furnace so as to maintain a spacing between said walls and said plurality of bands, said articulated arms being mounted at a distance from one to two meters from said corners of said furnace, each of said articulated arms forming an angle such that said walls of said furnace are pretensioned to cause mutually abutting ones of said walls to define obtuse angles in the cold condition of said furnace, said obtuse angles be selected such that the forces developed in said walls in response to heat generated in said furnace causes said obtuse angles to become right angles.

8. A boiler assembly according to claim 1, said member being a furnace hopper of rectangular'section, an additional plurality of horizontal bands surrounding and reinforcing said hopper, each of said bands of said additional plurality of bands consisting of four segments connected one with the other to form a rectangular figure, said segments being rigidly joined at their ends to form the'corners of said last-mentioned figure, said furnace hopper having outer walls joined together to define respective corners thereof, said hopper having a welded tube wall disposed therein, said walls of said hopper being joined so as to impart thereto a pretensioning which causes said hopper to bend at the corners thereof with heat so as to accommodate the thermal expansion of said tube wall, said walls of said hopper defining an opening slit at the bottom of said hopper, said walls being pretensioned in the region of said slit to take up the vertical difference expansion of said walls so as to cause the edges of said slit to form parallel straight lines when said hopper becomes heated,

9. A boiler assembly according to claim 1 wherein said boiler is a single-flue boiler comprising a furnace portion, having vertical walls, convection heat surface means disposed above said furnace portion, and an additional plurality of horizontal bands surrounding said heat surface means, said last-mentioned bands being frame-like and rigid, said heat surface means being welded to said vertical walls of said furnace portion, said heat surface means comprising inlet and outlet collectors, said collectors being subdivided at the regions of the corners of said additional plurality of horizontal bands so as to accommodate the heat expansion of said heat surface means. l

10. A boiler assembly according to claim 1 wherein said furnace is driven at underpressure and wherein said furnace comprises convection heat surface means, stuffing boxes mounted in the walls of said furnace for slidably passing said heat surface means therethrough. t 

1. A boiler assembly comprising a supporting frame structure, a boiler mounted on said frame structure and comprising gas-tight welded furnace walls, means suspending said walls at the top of the frame structure, said walls being arranged to form a furnace of a rectangular cross-section wherein means are provided for generating heat when the boiler is operating, a member connected to said walls and introducing a discontinuity therein, a plurality of horizontal bands surrounding said walls to take up the expansion and contraction forces developed therein because of the heat generated in the furnace, each of said horizontal bands consisting of four segments connected one with the other to form a substantially rectangular figure, said segments being rigidly joined at their ends to form the corners of said figure, at least one additional band being disposed in the region of said member, holding means connected to said furnace walls and to said one band at the corners thereof so as to causE said walls to take up the portion of said forces acting in the region of said member, force transfer means connected between said plurality of bands and said furnace walls for guiding the boiler body in said plurality of bands so as to pretension said walls of said furnace so as to cause said walls to define obtuse angles at the corners of said furnace when there is no heat being developed therein, said angles being selected so as to cause said angles to become right angles as well as to cause said walls to extend parallel to adjacent band segments when said furnace is heated.
 2. A boiler assembly according to claim 1, said holding means being movable intermediate members and said force transfer means being a plurality of sets of articulate arms, the arms of each set being connected between corresponding bands of said plurality of bands and said furnace walls.
 3. A boiler assembly according to claim 1, said holding means being hinged arms.
 4. A boiler assembly according to claim 1, comprising tie rods disposed behind said walls and connected to said holding means for taking up said portion of said forces.
 5. A boiler assembly according to claim 1, comprising tubular tie rods disposed behind said walls and connected to said holding means for taking up said portion of said forces, and means communicating with said tubular tie rods for passing steam therethrough.
 6. A boiler assembly according to claim 1, said one additional band consisting of four segments arranged to form a substantially rectangular figure and being open at the corners of said figure, said holding means comprising articulate arms connecting said segments at the respective corners of said figure to cause said furnace walls to take up said portion of said forces.
 7. A boiler assembly according to claim 1, said force transfer means comprising sets of articulated arms connecting respective ones of said plurality of bands with said furnace walls at the region of the corners of said furnace so as to maintain a spacing between said walls and said plurality of bands, said articulated arms being mounted at a distance from one to two meters from said corners of said furnace, each of said articulated arms forming an angle such that said walls of said furnace are pretensioned to cause mutually abutting ones of said walls to define obtuse angles in the cold condition of said furnace, said obtuse angles be selected such that the forces developed in said walls in response to heat generated in said furnace causes said obtuse angles to become right angles.
 8. A boiler assembly according to claim 1, said member being a furnace hopper of rectangular section, an additional plurality of horizontal bands surrounding and reinforcing said hopper, each of said bands of said additional plurality of bands consisting of four segments connected one with the other to form a rectangular figure, said segments being rigidly joined at their ends to form the corners of said last-mentioned figure, said furnace hopper having outer walls joined together to define respective corners thereof, said hopper having a welded tube wall disposed therein, said walls of said hopper being joined so as to impart thereto a pretensioning which causes said hopper to bend at the corners thereof with heat so as to accommodate the thermal expansion of said tube wall, said walls of said hopper defining an opening slit at the bottom of said hopper, said walls being pretensioned in the region of said slit to take up the vertical difference expansion of said walls so as to cause the edges of said slit to form parallel straight lines when said hopper becomes heated.
 9. A boiler assembly according to claim 1 wherein said boiler is a single-flue boiler comprising a furnace portion, having vertical walls, convection heat surface means disposed above said furnace portion, and an additional plurality of horizontal bands surrounding said heat surface means, said last-mentioned bands being frame-like and rigid, said heat surface means being welded to Said vertical walls of said furnace portion, said heat surface means comprising inlet and outlet collectors, said collectors being subdivided at the regions of the corners of said additional plurality of horizontal bands so as to accommodate the heat expansion of said heat surface means.
 10. A boiler assembly according to claim 1 wherein said furnace is driven at underpressure and wherein said furnace comprises convection heat surface means, stuffing boxes mounted in the walls of said furnace for slidably passing said heat surface means therethrough. 